The invention concerns magnetic couplings employing magnetic hysteresis and the use of such couplings or couplers as a slip-clutch in a power train in winding and unwinding mechanisms.
French Patent No. FR-1 602 519 describes a winding and unwinding mechanism using such couplers. Each coupler has two coaxial elements adapted to rotate relative to one another. One of these elements contains an inductor which develops an alternating multipolar magnetic field with its poles succeeding one another by symmetry of revolution about the axis of revolution. The other element is of ferromagnetic, preferably magnetically hard material which has not previously been magnetized. The inductor has electromagnets, or preferably permanent magnets. During the winding or unwinding process, the drive motor may be kept at normal speed, though the possibility for slipping exists at the receiving elements or followers relative to the drive or load elements. According to this document, the torque transmitted then remains virtually constant. However, experience has shown that at high slipping speeds, and particularly in the unwinding process, the torque transmitted increased greatly and in a troublesome way with the slipping speed. For example, the increase might be more than a relative +60% for slipping speeds of over 2000 revolutions per minute, in the case of winding and unwinding couplers.
Old British Patent No. GB-A-266 799 (1927) describes in particular electric motors with an induced element which is electrically non-conductive or hardly conductive. It is made of magnetic materials in divided form, possibly mixed with a non-conductive binder, leading to the virtual absence of Foucault currents. These armatures and motors are simple and inexpensive.
Applicants have attempted to perfect a magnetic coupler giving a transmitted torque which is almost or completely independent of the slipping speed.